Steam generator having improved steam heating sections arranged for parallel flow



April 1967 H. M. ECKERLIN A 98 STEAMGENERATOR HAVING IMPROVED STEAM HEATING SECTIONS ARRANGED FOR PARALLEL FLOW Filed Dec. 25, 1965 2 Sheets-Sheet 1 F "7 W5 W4 CONVECTION REHEATER SECTION wsik I 11 INVENTOR: HERBERT M. ECKERLIN AGENT April Filed Dec.

H M. ECKERLIN STEAM GENERATOR HAVING IMPROVED STEAM HEATING SECTIONS ARRANGED FOR PARALLEL FLOW 2 Sheets-Sheet 2 Fig.4

INVENTOR: HERBERT M. ECKERLIN AGENT United States Patent 3,312,198 STEAM GENERATOR HAVDIG IMPROVED STEAM HEATING SECTIONS ARRANGED FOR PARALLEL FLOW Herbert M. Eckerlin, Raleigh, N.C., assignor to Combustion Engineering, Inc., Windsor, Conn, a corporation of Delaware Filed Dec. 23, 1965, Ser. No. 515,880 6 Claims. (Cl. 122-406) The invention relates in general to large steam generators equipped with steam superheater and/or steam superheater and steam reheater. The invention is more specifically concerned with a steam generating furnace chamber having walls lined with upright fluid cooled tubes, and in which a portion of the tubular wall lining is sup plemented by superheater or reheater radiant wall heating surfaces.

In the design of large steam generators the ratio of the rated quantity of steam generated to the width of the furnace chamber is a major factor in achieving an economically attractive over-all unit design. This consideration favors a tendency towards the building of high capacity boilers having a relatively narrow furnace width. Several problems have become troublesome in the evolution of these boilers, especially in connection with the superheater or reheater radiant heating surfaces placed in the furnace Walls.

First, due to the narrow furnace width coupled with an increased steam generating capacity, the pressure drop in the steam heater radiant tubular wall section has risen to uneconomically high levels. To relieve this high pressure drop the use of tubes of increasingly larger diameter in the radiant steam heater section has become necessary. In many instances the tube diameters of the steam heater, for example a reheater, exceed the spacing from centerline to centerline of the waterwall tubes lining adjacent parts. of the furnace wall. Accordingly, since these oversized reheater tubes enter and leave the furnace wall from headers located outside the furnace chamber, undesirable construction problems have arisen, such as the necessity of excessively offsetting the tubes, difficulties in sealing the Wall against gas leaks, etc.

Furthermore, in these units the terminal temperature difference, i.e., the difference between the temperature of the combustion gases at the gas pass terminal end and the temperature of the fluid flowing through heat absorbing surfaces that are the last ones touched by these gases, approaches a level which violates good, economic design.

The present invention overcomes the above difficulties by dividing the steam heater such as superheater or reheater into two sections which are arranged for parallel flow, with one section constituting the radiant heat absorbing part lining a portion of the furnace wall, and the other section constituting a convection heat absorbing part located in the rear gas pass of the boiler. In this manner the physical characteristics of the radiant section such as tube diameter, tube spacing and number of tubes can be selected so as to conveniently accommodate the tube diameter and spacing of the waterwall tubes lining other parts of the furnace walls, without excessive and costly offsetting of tubes. Furthermore, these dimensions can now be chosen freely so as to limit the pressure drop through the reheater to an optimum and economic value. In addition, the temperature of the fluid leaving each parallel steam heater section can now be held within allowable limits by the proper selection of tube diameter and steam flow to avoid overheating of the radiant tube wall.

It is accordingly an important object of the invention to optimize the steam heater radiant wall design with respect to material selection such as diameter of tubes; with respect to construction such as elimination of excessive offsetting of tubes; and with respect to operation such as designing for desired pressure drop, by providing the radiant steam heater with a parallelly disposed convection section.

It is another important object of the invention to provide control means for a radiant wall steam heater permitting regulation of the flow through the radiant section, so as to control the tube metal temperature and the final temperature of the superheated steam, while at the same time accommodating the diameter and spacing of the radiant steam heater tubes to those of the existing waterwall tubes.

Other objects and advantages of the invention will become apparent from the following description of an illustrative embodiment thereof When taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a schematic representation of a steam generator equipped with a radiant wall reheater section and .a reheater low temperature convection section, and showing means for controlling the steam temperature by regulation of the respective steam flow through these sections;

FIG. 2 is an elevational view of the tubes lining the front furnace wall, and including the tubes of a radiant wall reheater section;

FIG. 3 is an elevational view of a radiant wall section of the reheater showing the tube and tube bends as repre sented by centerlines;

FIG. 4 is an elevational section through the front furnace wall when taken on line 44 of FIG. 2;

FIG. 5 is a plan section through the furnace wall when taken on line 55 of FIG. 4; and

FIG. 6 is a plan section through the furnace wall similar to that shown in FIG. 5, however, showing the reheater radiant wall tubes in staggered rows.

Referring now to the drawings wherein like reference characters are used throughout to designate like elements, the illustrative and preferred embodiment of the invention depicted therein includes a steam generator 10, comprising a furnace chamber 12 having walls lined with closely spaced water carrying tubes 14. The furnace 12 received fuel and air 'by way of burners 16 for burning and production of combustion gases. These hot gases rise in the furnace and are partially cooled by the furnace wall tubes including the tubes 18 of the radiant reheater wall section 19 which line the upper part of the front wall 20 of the furnace. These gases then sweep over the tubular heating surfaces of the final or finishing section 22 of the reheater, pass into a horizontal gas offtake duct 24 and flow downwardly through a rear gas pass 26. Gas duct 24 contains a high temperature superheater section 28, and rear pass 26 has located therein a low temperature superheater section 29 followed by a low temperature reheater convection section 30. After transferring heat to these heating surfaces the gases may pass over additional conventional heat exchangers such as an economizer and an air heater (not shown) and are then discharged into the atmosphere by a stack, not shown.

In a conventional reheat steam power plant of the type herein described the working fluid cycle comprises a feedwater source from which feedwater is conducted to the steam evaporating surfaces of the steam generator such as waterwall tubes 14. The evaporated steam then passes to a superheater such as low temperature superheater 29 and high temperature or finishing superheater 28, from whence the steam is conducted to a point of use such as the high pressure stage of a steam turbine, not shown. After having given up some of the thermal energy by expansion and temperature reduction, the steam is returned at lower pressure and temperature to a reheater for reheating, such as to low temperature reheater sections 19 and 3t and high temperature reheater section 22, and thence may be conducted to the low pressure stage of the turbine for final conversion of the thermal energy thereof Into mechanical and electrical energy.

In the steam generator illustratively shown in FIG. 1, the front wall 20 of the furnace 12 is lined with waterwall tubes 14. The upper part of the front wall 20 is, in addition, lined with the tubes 18 of the radiant wall reheater section 19. These tubes 18 originate in inlet header 32 which receives steam from the high pressure turbine stage by way of conduit 33, with these tubes passing through the furnace wall as shown in FIG. 4. The waterwall tubes 14 which are closely spaced in the lower portion of the furnace chamber 12, as shown in FIG. 2, are bifurcated at 34 to facilitate passage therebetween of tubes 18 which are then bent upwardly as shown in FIG. 4 and are suitably offset as shown in FIG. 3 to form a wall panel of closely spaced tubes located directly in front of the now widely spaced waterwall tubes 36 that have issued from bifurcates 34.

In accordance with the preferred embodiment of the invention as shown in FIGS. 2, 3 and 4 the diameter and spacing of the waterwall tubes 14 and those of the radiant reheater wall tubes 18 are substantially the same. Thus, only every other tube 18 passing between tubes 36 must be offset, however, with the offset dimensions of each tube being identical. A similar simplified tube arrangement is possible according to the invention at the points where the reheater tubes 18 pass through the tubes 38 forming the roof of the furnace chamber as shown in FIGS. 3 and 4. These tubes instead are being bifurcated as are tubes 14, are offset as shown at 39 to provide a space for two reheater tubes 18 to pass therethrough. Again, only one of a pair of tubes 18 must be offset with the offsets being identical.

Obviously, in accommodating the diameter and spacing of the reheater radiant wall tubes 18 to those of the waterwall tubes 14 as hereinabove described and giving, at the same time, due consideration to an economically acceptable pressure drop through reheater, operating requirements must also be considered such as total flow through the reheater and required fluid temperature rise. In accordance with the invention these requirements are conveniently satisfied in a most flexible manner by providing a reheater convection section 30 placed in the terminal portion of the rear gas pass 26, with the working fluid flow direction therethrough being in parallel relation with the direction of the working fluid flowing through radiant wall reheater tubes 18. To serve this end, a conduit 40 is provided for passing some of the steam from the high pressure turbine stage to the reheater convection section 30. This steam, after being reheated to a moderate extent by passing through reheater convection section 30, is thereafter conducted to a point 41 in the link 42 connecting the outlet of reheater radiant section 19 with the inlet of the finishing reheater 22. At this point 41 the relatively low temperature reheated steam flowing from convection reheater section 30 is intermixed with the relatively high temperature reheated steam flowing from radiant wall reheater section 19. The steam mixture then passes through finishing reheater 22 for heating to a final predetermined temperature before being conducted by way of conduit 44 to a point of use such as the low pressure stage of the steam turbine.

Thus it can readily be seen that the need of utilizing excessively large tubes and complicated tube offset arrangements in meeting existing pressure drop limitations is fully elimniated in accordance with the invention by supplementing a radiant wall reheater such as 19 with a parallelly arranged low temperature convection section such as 30. This permits considerable leeway in adapting the diameter and spacing of the tubes 18 of the reheater radiant wall section 19 to the diameter and spacing of the waterwall tubes 14 with the pressure drop requirement being satisfied through the addition of the reheater convection section 30.

To permit suitable allocation of the proper steam flow to the reheater radiant wall section 19 and to the reheater convection section 30, flow controlling devices are provided in conduits 33 and 40 such as valves 46 and 48, respectively. Also, a temperature indicating device 50 is installed to obtain indications of the temperature of the steam leaving radiant section 19 such as at point 51 in link 42. In addition, a temperature indicating device 52 is installed to obtain indications of the temperature of the reheated steam leaving finishing reheater section 22, such as at a point 53 in outlet conduit 44. These temperature indicating devices 50 and 52 are operationally connected by well known electrical, hydraulic, or other means to actuators 54 and 55 of valves 46 and 48, respectively. These connecting means are organized for transmission of control signals originating in temperature indicating devices 50 and/ or 52 to valve actuators 54 and 56 for regulating the flow of steam to reheater radiant section 19 and reheater convection section 30 in response to temperature variations of the reheated steam at the temperature measuring points 51 and/or 53.

Thus, to protect the reheater tubes 18 against heat damage, with an increase of the temperature at control point 51 above a predetermined allowable maximum temperature, valve 46 is actuated to permit an increased flow through reheater radiant section 19, and valve 48 is actuated to correspondingly reduce the flow through reheater convection section 30. Also, to maintain the reheated steam outlet temperature at 53 within predetermined limits, upon exceeding this limit impulses are transmitted from temperature recorder 52 to valve actuators 54 and 5s, respectively, to decrease the steam flow through reheater radiant section 19 and to increase the flow through reheater convection section 30. Conversely, upon a drop in temperature below the predetermined limit, impulses are transmitted from temperature recorder 52 to valve actuators 54 and 56, respectively, to increase the steam flow through reheater radiant section 19 and to decrease the flow through reheater convection section 36.

In FIG. 6 there is shown an arrangement of radiant reheater tubes wherein the tubes are disposed in two staggered rows 58, instead of one solid row as shown in FIG. 5. The arrangement shown in FIG. 6 permits a more uniform heat absorption by both waterwall tubes 36 and radiant reheater tubes 58.

While I have illustrated and described preferred embodiments of my invention, it is to be understood that such are merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

I claim:

1. In a vapor generator having an elongated furnace chamber defined by fluid cooled tube-lined walls, the combination of one section of said walls being lined with a plurality of upright tubes parallelly spaced, with said first tubes being cooled by the flow therethrough of a relatively low enthalpy fluid; another section of said walls adjoining said first section being lined with a plurality of upright second tubes parallelly spaced, with said second tubes being cooled by the flow therethrough of a first quantity of relatively high enthalpy fluid; means for producing a stream of hot gases for flowing over said tube-lined walls in heat exchange relation therewith and for partially cooling said gases; a gas offtake duct adjoining one end of said furnace chamber for receiving said partially cooled gases; first tubular heat absorbing surfaces provided in said duct for additional cooling of said gases; means for flowing a second quantity of high enthalpy fluid through said first tubular heating surfaces in parallel flow relation with the flow of said high enthalpy fluid through said second tubes; second heat absorbing surfaces provided in said gas stream in heat absorbing relation therewith, means for combining said first and said second quantity of high enthalpy fluid egressing from said second tubes of said other wall section and from said first tubular heat absorbing surfaces, respectively; means for flowing said combined flow through said second tubular heat absorbing surfaces; first means for controlling the flow of said first quantity of high enthalpy fluid and second means for controlling the flow of said second quantity of high en thalpy fluid; means for obtaining an indication of the temperature of said combined flow; and means for regulating said flow control means of at least one of said first quantity and of said second quantity of high enthalpy fluid in response to said temperature indication means.

2. In a vapor generator having an elongated furnace chamber defined by fluid cooled tube-lined walls, the combination of one section of said walls being lined with a plurality of upright tubes parallelly spaced, with said first tubes being cooled by the flow therethrough of a relatively low enthalpy fluid; another section of said walls adjoining said first section being lined with a plurality of upright second tubes parallelly spaced, with said second tubes being cooled by the flow therethrough of a first quantity of relatively high enthalpy fluid; means for producing a stream of hot gases for flowing over said tube-lined walls in heat exchange relation therewith and for partially cooling said gases; a gas ofltake duct adjoining one end of said furnace chamber for receiving said partially cooled gases; first tubular heat absorbing surfaces provided in said duct for additional cooling of said gases; means for flowing a second quantity of high enthalpy fluid through said first tubular heating surfaces in parallel flow relation with the flow of said high enthalpy fluid through said second tubes; second heat absorbing surfaces provided in said gas stream in heat absorbing relation therewith, means for combining said first and said second quantity of high enthalpy fluid egressing from said second tubes of said other wall section and from said first tubular heat absorbing surfaces, respectively; means for flowing said combined flow through said second tubular heat absorbing surfaces; first means for controlling the flow of said first quantity of high enthalpy fluid and second means for controlling the flow of said second quantity of high enthalpy fluid; means for obtaining an indication of the temperature of said first quantity leaving at least part of said'second tubes; and means for regulating said flow control means of at least one of said first quantity and of said second quantity of high enthalpy fluid in response to said temperature indicating means.

3. The combination as defined in claim 1, wherein said second tubular heat absorbing surface is located between said other wall section and said first tubular heat absorbing surfaces in the gas flow sense.

4. The combination as defined in claim 1, wherein the diameter of said first tubes equals the diameter of said second tubes.

5. The combination as defined in claim 1, wherein the spacing of said first tubes equals the spacing of said second tubes.

6. The combination as defined in claim 1, wherein the spacing of said second tubes is a multiple of the spacing of said first tubes.

References Cited by the Examiner UNITED STATES PATENTS 2,834,326 5/1958 Schaap 12 2-481 2,869,521 1/ 1959 Hardgrove 122479 2,902,982 9/1959 Rowand et al.

KENNETH SPRAGUE, Primay Examiner, 

1. IN A VAPOR GENERATOR HAVING AN ELONGATED FURNACE CHAMBER DEFINED BY FLUID COOLED TUBE-LINED WALLS, THE COMBINATION OF ONE SECTION OF SAID WALLS BEING LINED WITH A PLURALITY OF UPRIGHT TUBES PARALLELLY SPACED, WITH SAID FIRST TUBES BEING COOLED BY THE FLOW THERETHROUGH OF A RELATIVELY LOW ENTHALPY FLUID; ANOTHER SECTION OF SAID WALLS ADJOINING SAID FIRST SECTION BEING LINED WITH A PLURALITY OF UPRIGHT SECOND TUBES PARALLELLY SPACED, WITH SAID SECOND TUBES BEING COOLED BY THE FLOW THERETHROUGH OF A FIRST QUANTITY OF RELATIVELY HIGH ENTHALPY FLUID; MEANS FOR PRODUCING A STREAM OF HOT GASES FOR FLOWING OVER SAID TUBE-LINED WALLS IN HEAT EXCHANGE RELATION THEREWITH AND FOR PARTIALLY COOLING SAID GASES; A GAS OFFTAKE DUCT ADJOINING ONE END OF SAID FURNACE CHAMBER FOR RECEIVING SAID PARTIALLY COOLED GASES; FIRST TUBULAR HEAT ABSORBING SURFACES PROVIDED IN SAID DUCT FOR ADDITIONAL COOLING OF SAID GASES; MEANS FOR FLOWING A SECOND QUANTITY OF HIGH ENTHALPY FLUID THROUGH SAID FIRST TUBULAR HEATING SURFACES IN PARALLEL FLOW RELATION WITH THE FLOW OF SAID HIGH ENTHALPY FLUID THROUGH SAID SECOND TUBES; SECOND HEAT ABSORBING SURFACES PROVIDED IN SAID GAS STREAM IN HEAT ABSORBING RELATION THEREWITH, MEANS FOR COMBINING SAID FIRST AND SAID SECOND QUANTITY OF HIGH ENTHALPY FLUID EGRESSING FROM SAID SECOND TUBES OF SAID OTHER WALL SECTION AND FROM SAID FIRST TUBULAR HEAT ABSORBING SURFACES, RESPECTIVELY; MEANS FOR FLOWING SAID COMBINED FLOW THROUGH SAID SECOND TUBULAR HEAT ABSORBING SURFACES; FIRST MEANS FOR CONTROLLING THE FLOW OF SAID FIRST QUANTITY OF HIGH ENTHALPY FLUID AND SECOND MEANS FOR CONTROLLING THE FLOW OF SAID SECOND QUANTITY OF HIGH ENTHALPY FLUID; MEANS FOR OBTAINING AN INDICATION OF THE TEMPERATURE OF SAID COMBINED FLOW; AND MEANS FOR REGULATING SAID FLOW CONTROL MEANS OF AT LEAST ONE OF SAID FIRST QUANTITY AND OF SAID SECOND QUANTITY OF HIGH ENTHALPY FLUID IN RESPONSE TO SAID TEMPERATURE INDICATION MEANS. 